1sina=√15/4,cosa=±1/4∵a为第二象限角∴cosa=-1/4sin(a+π/4)=sinacosπ/4+cosasinπ/4=√30-√2/8sin2a=2sinacosa=-√15/8cos2a=cos²a-sin²a=7/8sin(a+π/4)/sin2a+cos2a+1=√30-√2/(-√15+15)=√2/...